The goal is to investigate the molecular mechanisms of transport across the colon. The methods involve the isolation of apical and basolateral plasma membranes and the use of radioactive tracers and spectrophotometric techniques to measure fluxes across these membranes. We will examine the kinetic characteristics of phosphorylation, ouabain binding, and sodium and potassium interactions of the Na/K ATPase and the mechanisms for nutrient transport in the basolateral membranes. In apical and basolateral membranes, we will investigate the ion permeability of conductive and nonconductive pathways using tracer fluxes and potential sensitive dyes. The effects of inhibitors of ion transport will be determined particularly the effects of amiloride on Na transport. Chemical group specific reagents will be used to attempt to label and identify the amiloride binding protein. Hormonal regulation of transport will be examined by isolation of membranes from animals treated so as to have high levels of aldosterone and from colon treated in vitro with aldosterone. These membranes will be studied for changes in ion permeability, enzyme activity and composition.